1. Field of the Invention
This invention relates to a method for the production of an absorbent polymer. More particularly, it relates to a method for the production of an absorbent polymer, which method is such that the absorbent polymer being formed within a reaction vessel avoids the occurrence of a hydrated gel of the absorbent polymer liable to adhere to the inner wall of the reaction vessel and, therefore, the absorbent polymer can be obtained stably and efficiently.
2. Description of the Prior Art
Heretofore, cross-linked polymers having acrylic acid or salts thereof as main components have been widely utilized for example, in disposable diaper, sanitary articles, agricultural/horticultural soil conditioners, and dehydrators.
The manner of producing such cross-linked polymers by an aqueous solution polymerization is disclosed in U.S. Pat. No. 4,625,001. In this method, an aqueous solution of a monomer is polymerized using a two-arm type kneader disclosed in FIGS. 1 and 2 of the U.S. Pat. No. 4,625,001 to obtain a hydrated gel-like polymer, possessing a cross-linked structure then drying and pulverizing the polymer thereby producing a cross-linked polymer. When the production is carried out by this method, however, an adhesive hydrated gel is joined during the course of polymerization of the monomer which adheres to the inner wall of the reaction vessel, to the extent of lowering the yield and, at the same time, impairing the efficiency of the work of removing the desired absorbent polymer from the reaction vessel. As the amount of the production increases, the deposit of the hydrated gel on the inner wall of the reaction vessel continues to grow. The reaction vessel, therefore, requires a periodic cleaning work. This fact seriously degrades the productivity of the conventional method. Trouble of this nature occurs particularly conspicuously on the portion of the inner surface of the reaction vessel which is repeatedly exposed to the reactants as well as the mainly inert gas.
For the solution of this problem, U.S. Pat. No. 4,625,001 discloses as a preferred embodiment, a method which comprises carrying out the polymerization reaction for the production of a hydrated gel polymer, possessing a cross-linked structure in a kneader lined with a fluorine resin coating. Japanese Patent Laid-Open SHO 57(1982)-63,305 discloses a method which comprises performing the polymerization reaction for the production of a water-soluble gel polymer in a vessel lined with a fluorine resin coating as a preferred embodiment. However, the fluorine resin coating cannot be called fully effective in precluding the adhesion of the gel polymer. The effectiveness of the fluorine resin coating in inhibiting the deposition is degraded as the number of cycles of reaction increases. Thus, these methods still entail the problem of requiring periodic repeated applications of the coating.
Japanese Patent Laid-Open SHO 54(1979)-10,387 discloses a method which carries out the polymerization reaction for the production of an aqueous gel polymer in a polymerization vessel possessing an electrolytically polished stainless steel surface. However, this method is inferior to the method relying on the fluorine resin coating in terms of the ability to preclude the deposition of the polymer.
An object of this invention is to provide a novel method for the production of an absorbent polymer.
Another object of the present invention is to provide a method for producing an absorbent polymer stably with high operational efficiency.